In manufacturing semiconductor devices such as LSI and Super-LSI or in manufacturing a liquid crystal display board, a pattern is made by irradiating a light to a semiconductor wafer or an original plate for liquid crystal display board; however, if a dust particle adheres to an exposure original plate (or a mask for lithography) used in this pattern creating stage, the dust particle absorbs light or bends it, causing deformation of a transferred pattern, roughened edges or black stains on a base, and leads to problems of damaged dimensions, poor quality, deformed appearance and the like.
For this reason, the above-mentioned lithography works are usually performed in a cleanroom, but even so, it is still difficult to keep the exposure original plate free of dust all the time; therefore, a counter-measure is practiced in which a pellicle having a high transmittance with respect to the light for exposure is bonded to the exposure original plate to shelter a part of the surface thereof. In this way, the dust particle is prevented from directly adhering to that surface of the exposure original plate but is caught on the pellicle membrane, and if, at the time of the lithography, the exposure light is focused on the pattern described on the exposure original plate the dust particle on the pellicle membrane does not partake in the image transferring.
The basic structure of a typical pellicle includes (i) a pellicle frame made of an aluminum alloy with its surface treated by a black colored alumite treatment and/or coated with an acrylic-based electrodeposition resin, (ii) a transparent pellicle membrane made of a material such as cellulose nitrate, cellulose acetate and a fluorine-containing polymer which transmits well such lights that are used in light exposure lithography and tensely adhered to an upper end face of the pellicle frame by means of an adhesive such as an acrylic resin, an epoxy resin and a fluorine-containing resin, and (iii) an agglutinant layer laid on a lower end face of the pellicle frame for bonding the pellicle to the exposure light original plate, the agglutinant layer being made of a polybutene resin, a polyvinyl acetate resin, an acrylic resin, a silicone resin or the like, and (iv) a liner laid over the agglutinant layer for protecting the agglutinant layer (ref. for example, IP Publications 1 and 2).
Also, in IP Publication 3 a pellicle for lithography is disclosed which is characteristic in that the four edges of the pellicle frame where the pellicle membrane-bonding end faces and the exposure original plate-bonding faces of the pellicle frame respectively meet the inner wall and the outer wall of the pellicle frame are chamfered, and that the chamfers on the side of the exposure original plate-bonding end face measure greater than C0.35 but not greater than C0.55.